Water dispersible moulds

Abstract

A water dispersible mould for making a casting, the mould comprising a water-insoluble particulate material-and a binder therefor, the binder including polyphosphate chains and/or borate ions. The invention also provides a process for making a water dispersible mould for making a casting, the process including the steps of: (a) providing a water-insoluble particulate material; (b) combining the particulate material with a binder including polyphosphate chains and/or borate ions, the chains and/or ions being dissolved in water; (c) forming, either during or after step (b), the particulate material and binder mixture into a desired shape; and (d) removing free water from the mixture. The polyphosphate chains may be derived from a water soluble phosphate glass and the borate ions may be derived from a soluble borate glass.

We claim: 
     
       1. A water-dispersible mould for making a casting, the mould comprising a water-insoluble particulate material and a binder therefor, wherein the binder contains at least one matrix former selected from the group consisting of polyphosphate chains derived from water-soluble phosphate glass and borate ions. 
     
     
       2. A water dispersible mould according to claim 1 wherein the said at least one matrix former in said binder is borate ions wherein said borate ions are derived from water-soluble borate glass. 
     
     
       3. A water dispersible mould according to claim 2 wherein said at least one matrix former in said polyphosphate claims derived from water-soluble phosphate glass or said borate ions wherein said borate ions are derived from water-soluble borate glass and wherein said water-soluble phosphate glass or said water-soluble borate glass has been partially devitrified. 
     
     
       4. A water dispersible mould according to claim 2 wherein said matrix former in said binder is in the form of an aqueous solution of at least one of said water-soluble glasses. 
     
     
       5. A water dispersible mould according to claim 2 wherein the binder has been mixed with the particulate material in the form of particles of the at least one water soluble glass and said at least one matrix former being formed by mixing water with the mixture of particulate material and glass particles. 
     
     
       6. A water dispersible mould according to claim 2 wherein the water soluble phosphate glass comprises from 30 to 80 mol % P 2  O 5 , from 20 to 70 mol % R 2  O, from 0 to 30 mol % MO and from 0 to 15 mol % L 2  O 3 , where R is Na, K or Li, M is Ca, Mg or Zn and L is Al, Fe or B. 
     
     
       7. A water dispersible mould according to claim 6 wherein the water soluble phosphate glass comprises from 58 to 72 wt % P 2  O 5 , from 42 to 28 wt % Na 2  O and from 0 to 16 wt % CaO. 
     
     
       8. A water dispersible mould according to claim 2 wherein the binder comprises at least 0.25% by weight, and the particulate material comprises up to 9.75% by weight, of the total weight of the particulate material and the binder. 
     
     
       9. A water dispersible mould according to claim 8 wherein the binder comprises from 0.5 to 25% by weight, and the particulate material comprises from 99.5 to 75% by weight, of the total weight of the particulate material and the binder. 
     
     
       10. A water dispersible mould according to claim 1 wherein the particulate material is foundry sand. 
     
     
       11. A water dispersible mould according to claim 1 wherein the mould is a core. 
     
     
       12. A process for casting a castable material, the process comprising making a water dispersible mould according to claim 1, pouring castable material into contact with the mould so as to adopt the surface shape of the mould, and dispersing the mould from the solid cast material by treating the mould with an aqueous liquid. 
     
     
       13. A process according to claim 12 wherein the castable material is liquid metal. 
     
     
       14. A process for making a water dispersible mould for making a casting, the process including the steps of: (a) providing a water-soluble particulate material;   (b) combining the particulate material with a binder wherein said binder contains at least one matrix former selected from the group consisting of polyphosphate chains derived from a water-soluble phosphate glass and borate ions, said at least one matrix former being dissolved in water;   (c) forming, either during or after step (b), the particulate material and binder mixture into a desired shape; and   (d) removing free water from the mixture.   
     
     
       15. A process according to claim 14 wherein the at least one matrix former have been derived from water-soluble glass selected from the group consisting of a water soluble phosphate glass, water-soluble borate glass or water-soluble phosphate glass and a water-soluble borate glass. 
     
     
       16. A process according to claim 15 wherein in step (b) the binder which is mixed with the particulate material is in the form of particles of the water soluble glass and wherein the polyphosphate chains, the borate ions or the polyphosphate chains and borate ions are formed by mixing water with the mixture of particulate material and particles of said water-soluble glass. 
     
     
       17. A process according to claim 16 wherein water is added in an amount of up to 13 % by weight based on the total weight of the mixture. 
     
     
       18. A process according to claim 15 wherein in step (b) the binder which is mixed with the particulate material is in the form of an aqueous solution of the at least one water soluble glass. 
     
     
       19. A process according to claim 15 wherein the water soluble phosphate glass comprises from 30 to 80 mol % P 2  O 5 , from 20 to 70 mol % R 2  O, from 0 to 30 mol % MO and from 0 to 15 mol % L 2  O 3 , where R is Na, K or Li, M is Ca, Mg or Zn and L is Al, Fe or B. 
     
     
       20. A process according to claim 19 wherein the water soluble phosphate glass comprises from 58 to 72 wt % P 2  O 5 , from 42 to 28 wt % Na 2  and from 0 to 16 wt % CaO. 
     
     
       21. A process according to claim 14 wherein in forming step (c) the particulate material and binder mixture is blown under pressure into a mould box thereby to shape the mixture into the desired shape. 
     
     
       22. A process according to claim 21 wherein the mould box is heated before the mixture is blown thereinto. 
     
     
       23. A process according to claim 21 wherein the mixture is blown by means of compressed air. 
     
     
       24. A process according to claim 21 wherein after the mixture has been blown into the mould box the mould box filled with the mixture is purged with compressed purging air. 
     
     
       25. A process according to claim 24 wherein the compressed purging air is at an elevated temperature. 
     
     
       26. A process according to claim 25 wherein the elevated temperature is from 50° to 90° C. 
     
     
       27. A process according to claim 24 wherein the compressed purging air removes the free, non-chemically bound, water from the mixture. 
     
     
       28. A process according to claim 21 wherein in step (d) water is removed from the mixture by heating. 
     
     
       29. A process according to claim 28 wherein the mixture is heated to a temperature in excess of 1000° C. to remove substantially all free, non-chemically bound water from the mixture. 
     
     
       30. A process according to claim 28 wherein the mixture is heated in a hot air oven after removal from the mould box. 
     
     
       31. A process according to claim 28 wherein the mould box is substantially transparent to microwaves and the mixture is heated in the mould box by microwaves. 
     
     
       32. A process according to claim 14 wherein the mould is a core. 
     
     
       33. A process according to claim 14 wherein in step (b) the binder comprises at least 0.25% by weight, and the particulate material comprises up to 99.75% by weight, of the total weight of the particulate material and the binder. 
     
     
       34. A process according to claim 32 wherein in step (b) the binder comprises from 0.5 to 25% by weight, and the material comprises from 99.5 to 75% by weight, of the total weight of the particulate material and the binder. 
     
     
       35. A process according to claim 14 wherein the refractory particulate material is foundry sand. 
     
     
       36. A process for making a water dispersible mould for making a casting, the process including the steps of: (a) providing a water-insoluble particulate material;   (b) combining the particulate material with a binder wherein said binder is derived from water and at least one glass selected from the group consisting of water soluble phosphate glass and water-soluble borate glass;   (c) forming, either during or after step (b), the particulate material and binder mixture into a desired shape; and   (d) removing free water from the mixture.